OSHA has estimated that approximately 5 million workers use respirators and further, that roughly 20 percent of all business establishments have employees that use respiratory protection. Given this prevalence, it is important that the effectiveness of different types of respirators be thoroughly characterized so that employees can be assured of adequate protection. The measurement of workplace protection factors (WPF) provides a way to evaluate the level of protection provided by respirators worn under actual conditions. However, there is a lack of WPF data available, particularly for gases and vapors. Although methods for measuring WPFs have previously been described, these studies have typically involved continuous sampling of aerosols. This project will focus on the development of an intermittent sampling system designed to measure the concentration of gases and vapors inside the respirator during inspiration. This approach addresses two potential problems associated with continuous sampling: biased results due to lower contaminant concentrations in exhaled air, and high humidity. The system will be based on a pressure transducer circuit that activates sampling pumps during inspiration. Solid granular adsorbent tubes will be used to trap the contaminants making the approach applicable to numerous gases and vapors. The pressure transducer circuit, pumps, and a data logger will be integrated into a single battery-powered unit measuring approximately 5"x5"x2.5" and weighing less than 2.5 lb. Interface circuitry will be developed to log heart rate and body temperature, thus allowing work rates and WPFs to be measured simultaneously. Laboratory evaluation of the sampling system will be conducted using an exposure chamber containing a headform connected to a breathing machine with half- and full-face respirators from two different manufacturers. Finally, three prototype units will be fabricated and field tested using volunteers in actual work settings. The proposed sampling system should be a valuable tool for investigators and would directly address research needs identified during the recent promulgation of the revised Respiratory Protection Standard and in the National Occupational Research Agenda (NORA) under the category of Research Tools and Approaches.